Botulism

Mary Dawn T. Co

Richard T. Ellison III

The name botulism is derived from the Latin term botulus for sausage. Justinus Kerner (1786–1862) first recognized the association between the mysterious “sausage poison” and paralytic illnesses in 1820. Clostridium botulinum, the etiologic agent of botulism, is an anaerobic, spore-forming organism that elaborates a neurotoxin that prevents the release of acetylcholine. Illness develops after toxin exposure, and patients present with a symmetric descending paralysis that characteristically begins with dysarthria, diplopia, dysphonia, or dysphagia. The most common botulism syndromes include food-borne, wound, and infant botulism. Botulism toxin is also now used therapeutically in neuromuscular and ophthalmologic disorders as well as a cosmetic enhancement tool, and cases of iatrogenic botulism have occurred. Although the majority of cases are due to infant botulism, food-borne botulism is considered a public health emergency as there is always a potential that a large number of individuals may have been exposed. Additionally, botulinum is a category A biological agent, and any case must initially be considered as potentially linked to a bioterrorist event (see Chapter 213).

Pathogenesis

C. botulinum is an anaerobic Gram-positive bacillus that produces heat-resistant spores that can survive boiling. Under conditions of an anaerobic environment, low acidity (pH greater than 4.6), and low temperature, the organism can germinate, grow, and produce a neurotoxin that itself is readily inactivated by heat (greater than 85°C for 5 minutes) [1].

Seven distinct antigenic neurotoxins (A through G) may be produced by C. botulinum but only four types—A, B, E, and F—are associated with human disease. Food-borne botulism occurs after the ingestion of preformed toxin in foods contaminated by spores. Wound botulism occurs when spores infect traumatized or contaminated skin. Infant botulism occurs in infants 3 to 26 weeks old after intestinal colonization by C. botulinum [2]. Botulism of undetermined etiology occurs in adults whose intestinal flora has been altered or whose gastric barrier has been compromised because of intestinal surgery, gastric achlorhydria, or antibiotic therapy [2,3].

All botulinum toxins have the same mechanism of action [2]. The toxin is carried via the bloodstream to the neuromuscular junction where it binds irreversibly and thereby produces paralysis. However, it does not affect the central nervous system or the adrenergic nervous system [1]. The toxin is a zinc-containing endopeptidase that cleaves to specific sites on three proteins (VAMP, SNAP25, syntaxin), interfering with the release of acetylcholine [4].

Epidemiology

There have been approximately 20 cases of food-borne botulism yearly in the United States, with the majority of cases caused by toxin type A (50%), followed by toxin type E (37%), and then toxin type B (10%) [5]. Food-borne botulism has traditionally been associated with home-processed foods. However, an increasing number of cases have been associated with commercially prepared foods that have inadvertently been processed in a manner that allowed the production of the toxin.

Wound botulism has primarily been seen in intravenous drug users who present with cranial nerve palsies in the setting of abscesses from heroin use [6]. California has accounted for over 75% of U.S. cases, with an epidemic noted in individuals injecting black tar heroin [7].

Iatrogenic botulism has rarely developed after botulinum toxin (Botox) has been injected for cosmetic or neurologic purposes [8,9]. Although the normal concentration of botulinum toxin A in the therapeutic preparation allows for a large margin of safety with minimal treatment side effects, therapeutic doses have been reported to cause generalized muscle weakness with widespread electromyogram (EMG) abnormalities typical of botulism [10]. In addition, four individuals have contracted botulism after receiving unlicensed preparations of botulinum toxin for cosmetic purposes [11].

Botulism toxin is the most poisonous substance known to man with 1 g of toxin able to potentially kill 1 million people [9]. Given its ease of production and transport, it is a major bioterrorism threat and is classified as a category A biological agent. Botulism toxin was used as a bioweapon in the 1930s by the Japanese military who fed cultures of C. botulinum to prisoners during that country’s occupation of Manchuria [12]. Aerosols derived from botulism toxin were also dispersed in Japan on at least three different occasions by a Japanese cult, although for unclear reasons these terrorist attempts failed [12] (see Chapter 213).

Clinical Manifestations

Clinical manifestations of all forms of botulism are similar. Cardinal features include (a) cranial nerve palsies, (b) descending paralysis, (c) symmetry in symptoms, (d) absence of fever, (e) clear sensorium, and (f) lack of sensory findings [1]. Food-borne botulism may be preceded by gastrointestinal symptoms such as cramps, nausea, vomiting, and diarrhea [2,12]. Infant botulism is usually characterized by a history of constipation and feeding difficulties [2,12].

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